A wide variety of articles that incorporate the phenomenon of retroreflectivity have been developed for a wide array of uses. Retroreflective articles have the ability to return a substantial portion of incident light back towards the light source. This unique ability has promoted widespread use of retroreflective safety articles. Besides traffic and warning signs and the like, a wide variety of clothing and similar articles such as backpacks, and the like have incorporated retroreflective articles into them. Persons who work or exercise near motor vehicle traffic need to be conspicuously visible so that they do not get struck by passing motor vehicles. When retroreflective articles are worn, the retroreflectivity highlights a person's presence by retroreflecting light from motor vehicle headlamps.
Retroreflective articles generally include a polymeric binder layer, an optical lens element layer, and a reflective layer. For example, the optical lens element layer can be a layer of microspheres partially embedded in the binder layer, and the reflective layer can be disposed on the embedded portions of the microspheres. The reflective layer can be aluminum or silver (e.g., for applications requiring high reflectivity) or a dielectric mirror (e.g., for applications not requiring high reflectivity). Light striking the front surface of the retroreflective article passes through the microspheres and is reflected by the reflective layer to re-enter the microspheres where the light's direction is then altered to travel back towards the light source. Thus, for example, when a vehicle's headlamps strike a retroreflective article, some of the light from the headlamps is reflected back to the driver of the vehicle.
It is generally not necessary, or even desirable, that an entire worn article be retroreflective, so retroreflective appliqués can be used. These retroreflective appliqués can then be attached to an article of clothing or other article to prepare a retroreflective article. In some instances, retroreflective appliqués have been made by partially embedding a microsphere layer in a thermoplastic carrier web, applying a reflective material over the microspheres' protruding portions, and then forming a binder layer over the coated microspheres. A pressure sensitive adhesive can be applied on the binder layer's back surface, and a release liner can be placed over the adhesive until it is desired to apply the appliqué to a substrate. The completed appliqué (also sometimes referred to as a transfer article or transfer sheet) can be supplied to a garment assembler in this form, and the garment assembler can secure the appliqué to an article of clothing by removing the release liner and adhering the appliqué to an outer surface of the article of clothing. The carrier can then be separated from the appliqué to expose the microspheres so that the appliqué can retroreflect light.
A number of retroreflective articles have been prepared and described. For example, in U.S. Pat. No. 6,361,850 (Billingsley et al.), retroreflective articles are described employing a colored layer disposed between microspheres and a reflective layer. U.S. Patent Publication No. 2011/0292508 (Huang et al.) describes an exposed lens retroreflective articles that includes a binder layer, a layer of spaced apart microspheres that are partially embedded in the binder layer, a penetrated colored layer that is located between the spaced apart optical elements, and a reflective layer that is located functionally behind the layer of optical elements and the penetrated colored layer. U.S. Pat. No. 3,700,305 describes retroreflective constructions containing microspheres with adjacent dielectric mirrors.
Originally, retroreflective materials were generally all silver in color based on the metal reflective layer employed. As the need arose for retroreflective articles that were colored other than silver, the retroreflective nature of the articles suffered. Therefore, there remains a need for colored retroreflective articles that have increased retroreflective properties.